The present invention generally pertains to injection molding of plastic products and is particularly directed to an improvement in a self-aligning mold for injection molding of hollow plastic products.
A self-aligning mold is described in U.S. Pat. No. 3,375,554. The mold described therein includes a cavity mold part and a core mold part mounted for axial movement with respect to each other, and defining a mold cavity therebetween for forming the hollow plastic product. There is an axially positioned gate in the cavity mold part for admitting injected plastic into the mold cavity. The mold cavity includes a circular base region for forming the bottom portion of the product and a region that extends from the base region for forming the side wall of the product. The base region includes a throttle that is concentric with respect to the gate but varies circumferentially in width when the mold parts are not axially aligned to thereby admit more injected plastic material into the portion of the region that is the thinnest as a result of said axial misalignment for the purpose of forcing the mold parts into alignment. Unfortunately, the path of least resistance for the plastic material flowing into the region is generally lateral, and as a result the plastic material flowing into the thinnest portion of the region from the throttle moves around to the thickest portion of the region and maintains a significant portion of the axial misalignment of the mold parts.